Many different compression garments have been built to provide compression therapy for the treatment of circulatory disorders such as edema, lymphedema and various venous diseases. Typically, these compression garments fall into two broad categories: elastic and inelastic.
Elastic compression garments such as compression stockings, both circular and flat knit, are based on the use of elastic fibers such as spandex or latex. It is this elastic fiber that enables the stocking to provide compression and also to stretch in order to apply the stocking to the limb. Because of the elastic nature of the stocking design, stockings provide a consistent or static compression to the limb; when an individual changes position, such as moving from supine to standing, the limb circumference changes. The elastic nature of the stocking stretches to accommodate the change in circumference and maintains a fairly consistent compression level regardless of position or movement. This is particularly beneficial when a patient experiences a reduction in limb size due to the removal of excess edema in the treated limb. However it also requires that the compression stocking be removed when in a supine position (sleeping) because a consistent high compression level may result in pain in the limbs due to the decreased venous pressure.
Inelastic compression, as the name suggests, is the opposite of elastic compression in that the products do not stretch when circumference changes occur as the result of body movement. What occurs when the body is in movement is that the actual compression level under the inelastic compression system will rise and fall, thus creating a dynamic compression system. This change in compression with inelastic compression systems has been demonstrated to have dramatic effects in improved venous hemodynamics and edema reduction. Inelastic compression is achieved with Unnas boot bandages, short-stretch bandages, multi-layer bandages as well as with inelastic, adjustable wraps. These compression systems can also be worn 24 hours a day because the compression level is only at its highest when needed while standing, moving and fighting the effects of gravity on the circulatory system. The compression level is at its lowest while supine and venous pressure has decreased. While bandage systems do provide a dynamic compression effect their main drawback is that they do not adjust with reductions in the limb size and as such over the course of wear the compression level drops. This requires that the bandages be removed and reapplied quite often to maintain adequate compression for treatment. Unique systems like CircAid® Compression garments have instantly adjustable bands so the compression level can be easily adjusted to accommodate changes in limb volume.
In recent years a measurement of the elasticity or stiffness of a compression system has been accepted and is referred to as the Static Stiffness Index. The Static Stiffness Index (SSI) is defined as the absolute change in compression applied to the limb by the compression garment when the user changes posture from the standing to supine position. The pressure applied while standing is often termed working pressure and while supine is termed resting pressure. Systems with an absolute working-resting pressure difference of less than 10 mmHg are qualified as elastic systems. Those with a difference greater than 10 mmHg are considered inelastic systems.
All compression systems can now be defined by not only the absolute compression level they provide but also by amount that the compression level fluctuates during activity or Static Stiffness Index. For example an elastic stocking may provide a compression level of 20-30 mmHg but has an SSI of 5 mmHg, whereas an inelastic wrap may also provide a compression level of 20-30 mmHg but have an SSI of 20 mmHg. It has been proven that therapeutic differences exist between these two systems. While the elastic system may be more preferable to the user because it is more consistent with limb volume changes and requires less adjustments, their condition may dictate the need for improved circulatory performance provided by the inelastic garment. If a compression garment existed that provided 20-30 mmHg and a SSI of 10 mmHg perhaps this would be the best combination of benefits for this particular patient. However, this compression garment may not exist forcing a decision to be made from the garments available.
To date by in large most products have only been defined and prescribed by the target compression level they provide and generically termed elastic or inelastic. The working and resting pressure levels they provide cannot be changed. Some compression garments have been designed to provide instantly adjustable compression levels to accommodate multiple prescription compression levels but the Static Stiffness Index of these garments remains relatively unchanged. A compression system has yet to be designed where the user can instantly adjust the static stiffness index in the garment or a portion of the garment to a prescribed level to meet their unique needs.